The present invention relates to exposure analysis systems to calibrate induction heating processes used in container sealing, metal hardening or annealing, and, more specifically, to magnetic field exposure sensors used in those exposure analysis systems.
Induction heating processes are used in-a variety of applications from sealing of bottles for pharmaceuticals to induction hardening of metals and annealing of parts. The process in the factory must be monitored for proper performance and for quality control statutory requirements. If the process parameters are not within specifications, the consequences could be very damaging.
In a bottle sealing process several problems can occur. Underexposure can cause a weak or incomplete seal resulting in an inability to keep out contaminants such as bacteria or viruses which could be fatal. Overexposure causes excessive heat in the foil layer which can cosmetically char the paper layer in contact with it or even degrade the plastic container.
Similarly, in an induction hardening process, the temper and surface hardness of the treated parts may not meet specifications, resulting in premature wear or catastrophic failure. In an annealing process, residual co stresses in the parts can cause failure with costly consequences.
Since induction heating processes involve the use of high frequency In (HF) magnetic fields, prior art in the measurement of this type of magnetic radiation is of some relevance. U.S. Pat. No. 3,914,689 of Wright disclose a self powered temperature-compensated rectifier for measuring current to assess the power in radio frequency waves; it does not require an additional source of power. French Patent No. 76 15704 of Bourgeois describes a method and an apparatus for measuring the magnetic vector, of an electromagnetic wave by incorporating a Faraday shield to exclude the electric field. U.S. Pat. No. 4,659,984 of Doss describes a passive integrating electromagnetic field dosimeter incorporating the use of an electrochemical cell. U.S. Pat. No. 5,432,437 of Turner relates to an exposure meter for use with induction heat sealing of containers. By using bottle caps with imbedded sensor coils and other apparatus, either integrated exposure values or instantaneous magnetic field readings can be indicated or transmitted to adjacent indicating meters.
Other background art includes PCT publication Ser. No. 82/12593 of Payne for a device which senses temperature variations in a material in a welding process and U.S. Pat. No. 3,604,882 of Seyfried for a sensing coil for analyzing induction heating and regulating voltage applied thereto. U.S. Pat. No. 3,914,689 of Wright describes a current measuring device, U.S. Pat. No. 4,634,969 of Edlin for a magnetic field safety probe to alert personnel, and U.S. Pat. No. 4,684,554 of Ou-Yang for a sealable container material.
However, there are inherent limitations with the prior art. For example, instantaneous readings or integrated exposure readings, such as described in Turner ""437, do not suffice to analyze the operation of induction heating equipment in a comprehensive manner.
Therefore, it is an object of the present invention to provide comprehensive exposure analysis of induction heating equipment to predict its accurate operation.
It is also an object of the present invention to sense the magnitude of a magnetic field produced by current flowing in an induction heating coil with a compact sensor that can include circuitry to process the sensed parameter and/or transmit the sensed parameter or processed data to a remote device.
It is also an object of the present invention to sense the magnitude of a magnetic field produced by current flowing in an induction heating coil over time by providing a signal proportional to the peak value of the magnetic field.
It is a further object of this invention to convert this signal to digital form and to store the digital values in a digital storage device.
It is another object of this invention to convert this signal using a voltage-to-frequency converter.
It is yet another object of this invention to transmit the data to a remote receiver by RF wireless transmission.
It is still another object of this invention to transfer the stored digital data to a computer or display device by a wire connection after the data have been collected.
It is also an object of this invention to use power supplied by the measured field to convert and store and/or to transmit the collected data.
It is further an object of this invention to provide multiple output of the data as field strength versus time, total energy, or average energy, as desired, from a single collection operation.
It is also an object of this invention to use multiple sensing coils to scan wider areas and to detect power from several points simultaneously.
It is yet another object of this invention to use a multi-channel analog-to-digital converter and a single microprocessor to accumulate data from several sensing coils simultaneously.
It is yet another object of this invention to improve over the limitations and disadvantages of the prior art.
In keeping with these objects and others which may become apparent, the present invention includes a high frequency magnetic field exposure sensor suitable for use in the induction heat sealing, hardening, or annealing of a member, during which operation each member passes beneath an induction coil.
The sensor of the sensing apparatus of the present invention includes a magnetic field sensing coil designed to be exposed to the same high frequency (HF) magnetic flux as the member receives during the induction heating operation.
A signal is produced proportional to the peak value of the magnetic field, as picked up by the sensing coil, and an overall power profile is detected by the sensing coil. The signal and power profile are converted into digital data and the data is stored in a digital storage device. The data are transmitted to a remote receiver, then transferred from the receiver and processed.
The sensing apparatus of the present invention preferably includes a power supply of different configurations, such as a means for using power from the measured field for the sensor, a rechargeable battery, or a replaceable battery.
When power is derived from the measured field, a capacitor is used, acting as an accumulator.
The apparatus may also provide multiple output of the data as field strength versus time, total energy, and average energy from a single collection operation. Multiple sensing coils may be used to scan wider areas and to detect power from several points simultaneously.
In addition, the analog-to-digital converter may be a multi-channel analog-to-digital converter using a single microprocessor to accumulate data from several sensing coils simultaneously.
Furthermore, the sensor apparatus may have a field presence detector for constantly monitoring for the presence of a magnetic field, maintaining the sensor in a sleep mode in the absence of a magnetic field, and producing a wake-up signal when a magnetic field appears, so it is only used intermittently, when needed.
Moreover, the obtained data may be transmitted by a wireless transmitter, or a non-volatile storage apparatus and a port for later access to the data.
Furthermore, the transmitter may be a real time transmitter of data which transmits data as the data in question are measured, wherein the receiver stores the measured data in a storage device located at the receiver.
In an alternate embodiment, the present invention includes a high frequency magnetic field exposure sensor, but uses a voltage-to-frequency converter. This sensor is also suitable for use in an induction heat sealing process for heat sealing the metal foil wad elements in a closure to a container to be closed by the closure, during which operation each closure passes beneath an induction coil of an induction heat sealing apparatus.
This sensor includes a magnetic field sensing coil designed to be exposed to the same high frequency (HF) magnetic flux as the metal foil wad elements of the closures receive during the induction heat sealing operation.
A signal is produced proportional to the peak value of the magnetic field as picked up by the sensing coil and an overall power profile as detected by the sensing coil.
The signal and the resultant power profile are converted into a frequency modulated radio frequency signal, which is transmitted to a remote receiver in real time. Then the signal is converted into digital data, which are stored in a digital storage device and transferred to a means for processing the data.
The invention may also have a power supply of different configurations, such as a means for using power from the measured field for the sensor, a rechargeable battery, or a replaceable battery. Moreover, the transmitting means may be a wireless transmitter.
In general, the present invention provides several exposure analysis systems with accurate power profiles and other important information to calibrate induction heating processes used in container sealing for pharmaceuticals, or induction metal hardening or annealing of parts.